Dielectrics are widely applied to capacitors, semiconductor devices, optical fibers, etc. For example, barium titanate, which has a perovskite structure, has a very high relative dielectric constant and is thus widely used as a dielectric material for multilayer ceramic capacitors.
Thermistors whose electrical resistance decreases with increasing temperature include NTC (negative temperature coefficient) thermistors whose electrical resistance slowly decreases with increasing temperature and CTR (critical temperature resistor) thermistors whose resistance abruptly drops once a certain temperature is exceeded. Sintered bodies of oxides of nickel, manganese, iron etc. are used as NTC thermistors. Sintered bodies produced by sintering an oxide of vanadium with an additive are used as CTR thermistors.
However, NTC thermistors have limited applications because the decrease in electrical resistance with increasing temperature is slow. Currently used CTR thermistors generally lack a sufficiently high initial electrical resistance value and are available only in a small variety of types; hence, these CTR thermistors may fail to operate depending on the resistance value of a circuit, thus having a limited use. Additionally, for the CTR thermistors, the change in electrical resistivity with increasing temperature is on the order of 103 times, and this causes problems such as low performance of a control circuit such as a thermostat. Further, when these thermistors are used as thermometers, there are the following problems: an NTC thermometer fails to perform sufficiently accurate temperature detection because of the slow decrease in electrical resistance of the NTC thermistor, whereas a CTR thermistor undergoes an abrupt resistance change in a narrow temperature region and thus has markedly reduced sensitivity as a thermometer outside a specific temperature region.
Piezoelectric materials, which are a class of dielectric materials, are inverse piezoelectric-type electrostrictive materials which experience strain upon application of electric field, and are widely used, for example, in actuators based on electrical-mechanical energy conversion. For example, lead zirconate titanate (PZT) is used as such an electrostrictive material (Non Patent Literature 1). In the case of typical already-developed electrostrictive materials, including those of the inverse piezoelectric type, the voltage application direction and the actuation direction are the same, and means such as a gear needs to be incorporated in order to enable operation in any other direction.
The present inventors conducted various investigations in an attempt to produce an ionic solid having an absolutely new function and have successfully created [Au4Co2(dppe)2(D-pen)4](ClO4)2.qH2O. This ionic solid has been found to be a charge-separated ionic solid which, unlike naturally occurring ionic solids consisting of pairs of ions, is formed of ionic clusters and is held in a solid state by non-coulombic force (Non Patent Literature 2).